What is the amplitude of $y=-4\cos(5x-9)-7$ ?
Answer: Amplitude in sinusoids of the form $y=a\cos(bx+c)+d$ The amplitude of a sinusoid of the form $y={a}\cos(bx + c) + d$ is equal to $|{a}|$. [How can we justify this given our graphical understanding of amplitude?] Finding the amplitude The amplitude of $y= {-4}\cos(5x-9)-7$ is $|{-4}|=4$.